The present invention concerns the field of radiology apparatus and, in particular, the assembly of such an apparatus.
A radiology apparatus used, for example, in mammography, RAD or RF conventional radiology and neurological or even vascular (peripheral or cardiac) radiology generally comprises: an X-ray tube and a collimator for forming and delimiting an X-ray beam; an image receiver, generally a radiological image intensifier and a video camera, or even a solid-state detector; a positioner carrying the X-ray tube and collimator assembly on one side and image receiver on the other, movable in space on one or more axes, and a table for supporting a patient. An example of such an apparatus is disclosed in EP-A-972,490 and the apparatus has use in x-ray imaging.
An X-ray tube mounted, for example, in a medical radiology apparatus comprises a cathode and an anode, both contained in a vacuum-tight envelope, for electric insulation between the two electrodes. The cathode produces an electron beam which is received by the anode on a small surface constituting a focus from which the X-rays are emitted.
On application of a high voltage by a generator at the terminals of the cathode and anode, a so-called anode current is established in the circuit through the generator producing the high voltage. The anode current crosses the space between the cathode and anode in the form of an electron beam which bombards the focus.
In order to obtain a high-energy electron beam, the electrons are accelerated by an intense electric field produced between the cathode and anode. For that purpose, the anode is brought to a very high positive potential in relation to the cathode. That potential can exceed 150 kV. To produce those potentials, high-voltage supply devices are used.
A part of the X-ray emission from the focus crosses the envelope and then the window of the casing. The window being of small dimensions, the cathode, anode and window have to be mounted in given relative positions that are precise and reproducible. Furthermore, the collimator is mounted outside the casing and is crossed by the X-ray beam. As a result, the position of the focus and the position of the axis of propagation of the X-ray beam, in other words, the position of the X-ray beam, have to be perfectly defined, notably, in relation to the casing. The position of the point of emission or focus of the X-ray beam is determined by three translations and three rotations of the X-ray tube in relation to the casing in a three-dimensional reference. Two of the positions in translation and two of the positions in rotation are obtained by design. However, the position in translation along the axis of rotation of the anode and the position in rotation on the same axis require adjustments requiring highly skilled labor, a considerable time and tools. In particular, it often proves indispensable to carry out X-ray emissions following which the apparatus is disassembled in order to perfect the adjustment and is reassembled, and so on until obtaining the desired positioning making it possible to satisfy radiation protection standards and to obtain good-quality images. Such an apparatus is disclosed in WO A 97/44809.